1. Field of the Invention
This invention relates generally to a high pressure tank and, more particularly, to a high pressure tank including an outer fiber composite layer having a first strain gauge and an inner liner layer having a second strain gauge, where the first and second strain gauges identify a pressure where the inner liner layer begins to shrink and separate from the outer layer.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cell systems as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
Typically hydrogen gas is stored in a compressed gas tank under high pressure on the vehicle to provide the hydrogen necessary for the fuel cell system. The pressure in the compressed tank can be 700 bar or more. In one known design, the compressed tank includes an inner plastic liner that provides a gas tight seal for the hydrogen gas, and an outer carbon fiber composite layer that provides the structural integrity of the tank. At least one pressure regulator is typically provided that reduces the pressure of the hydrogen gas within the tank to a pressure suitable for the fuel cell system.
If the pressure within the tank falls below a certain value, the inner liner layer may begin to shrink and separate from the outer layer. This separation could cause inner liner damage and loss of leak tightness, and thus must be avoided. A current solution to avoid this separation is to maintain a high of enough pressure within the tank to prevent inner liner layer shrinkage. For current tank designs, a minimum pressure of 20 bar must be maintained in the tank to prevent the inner liner layer from shrinking and separating from the outer structural layer.
Pressure sensors are provided within the tank to provide a measurement of the pressure within the tank. Because the pressure sensors employed in these types of tanks need to provide a reasonably accurate pressure measurement over a range of about 1000 bar, and they need to be relatively inexpensive, they typically have an accuracy of about 1.5%, which gives an accuracy of +/−15 bar. Further, considering the measurement requirements of the sensor wiring over the entire temperature range that the tank may encounter typically provides a measurement accuracy of +/−35 bar, which is added to the 20 bar to provide the desired safety margin. Thus, hydrogen discharge from the tank needs to be stopped at a tank pressure sensor reading of about 55 bar resulting in about 5% of the hydrogen gas within the tank not being usable for vehicle operation.